Genetic Variants of the Renin-Angiotensin-Aldosterone System and Reverse Remodeling After Cardiac Resynchronization Therapy

Dyssynchronous Heart Failure: A Clinical Review

PURPOSE OF THE REVIEW

Dyssynchrony occurs when portions of the cardiac chambers contract in an uncoordinated fashion. Ventricular dyssynchrony primarily impacts the left ventricle and may result in heart failure. This entity is recognized as a major contributor to the development and progression of heart failure. A hallmark of dyssynchronous heart failure (HF_d) is left ventricular recovery after dyssynchrony is corrected. This review discusses the current understanding of pathophysiology of HF_d and provides clinical examples and current techniques for treatment.

RECENT FINDINGS

Data show that HF_d responds poorly to medical therapy. Cardiac resynchronization therapy (CRT) in the form of conventional biventricular pacing (BVP) is of proven benefit in HF_d, but is limited by a significant non-responder rate. Recently, conduction system pacing (His bundle or left bundle branch area pacing) has also shown promise in correcting HF_d. HF_d should be recognized as a distinct etiology of heart failure; HF_d responds best to CRT.

Cardiac dyssynchrony and response to cardiac resynchronisation therapy in heart failure: can genetic predisposition play a role?

Cardiac resynchronisation therapy (CRT) is an accepted treatment for heart failure patients with depressed left ventricular (LV) function and dyssynchrony. However, despite better clinical outcome and improved cardiac function after CRT in the majority of eligible heart failure patients, a large proportion of implanted patients do not seem to benefit clinically from this therapy. In this review we consider whether genetic factors may play a role in modulating response to CRT and summarise the few genetic studies that have investigated the role of genetic variation in candidate genes.

Identification of Genetic Markers for Treatment Success in Heart Failure Patients

Background—

Cardiac resynchronization therapy (CRT) can improve ventricular size, shape, and mass and reduce mitral regurgitation by reverse remodeling of the failing ventricle. About 30% of patients do not respond to this therapy for unknown reasons. In this study, we aimed at the identification and classification of CRT responder by the use of genetic variants and clinical parameters.

Methods and Results—

Of 1421 CRT patients, 207 subjects were consecutively selected, and CRT responder and nonresponder were matched for their baseline parameters before CRT. Treatment success of CRT was defined as a decrease in left ventricular end-systolic volume >15% at follow-up echocardiography compared with left ventricular end-systolic volume at baseline. All other changes classified the patient as CRT nonresponder. A genetic association study was performed, which identified 4 genetic variants to be associated with the CRT responder phenotype at the allelic ( P <0.035) and genotypic ( P <0.031) level: rs3766031 ( ATPIB1 ), rs5443 ( GNB3 ), rs5522 ( NR3C2 ), and rs7325635 ( TNFSF11 ). Machine learning algorithms were used for the classification of CRT patients into responder and nonresponder status, including combinations of the identified genetic variants and clinical parameters.

Conclusions—

We demonstrated that rule induction algorithms can successfully be applied for the classification of heart failure patients in CRT responder and nonresponder status using clinical and genetic parameters. Our analysis included information on alleles and genotypes of 4 genetic loci, rs3766031 ( ATPIB1 ), rs5443 ( GNB3 ), rs5522 ( NR3C2 ), and rs7325635 ( TNFSF11 ), pathophysiologically associated with remodeling of the failing ventricle.

Race, common genetic variation, and therapeutic response disparities in heart failure

Because of its comparatively recent evolution, Homo sapiens exhibit relatively little within-species genomic diversity. However, because of genome size, a proportionately small amount of variation creates ample opportunities for both rare mutations that may cause disease as well as more common genetic variations that may be important in disease modification or pharmacogenetics. Primarily because of the East African origin of modern humans, individuals of African ancestry (AA) exhibit greater degrees of genetic diversity than more recently established populations, such as those of European ancestry (EA) or Asian ancestry. Those population effects extend to differences in frequency of common gene variants that may be important in heart failure natural history or therapy. For cell-signaling mechanisms important in heart failure, we review and present new data for genetic variation between AA and EA populations. Data indicate that: 1) neurohormonal signaling mechanisms frequently (16 of the 19 investigated polymorphisms) exhibit racial differences in the allele frequencies of variants comprising key constituents; 2) some of these differences in allele frequency may differentially affect the natural history of heart failure in AA compared with EA individuals; and 3) in many cases, these differences likely play a role in observed racial differences in drug or device response.

Pharmacogenomics in heart failure: where are we now and how can we reach clinical application?

Heart failure is becoming increasingly prevalent in the United States and is a significant cause of morbidity and mortality. Several therapies are currently available to treat this chronic illness; however, clinical response to these treatment options exhibit significant interpatient variation. It is now clearly understood that genetics is a key contributor to diversity in therapeutic response, and evidence that genetic polymorphisms alter the pharmacokinetics, pharmacodynamics, and clinical response of heart failure drugs continues to accumulate. This suggests that pharmacogenomics has the potential to help clinicians improve the management of heart failure by choosing the safest and most effective medications and doses. Unfortunately, despite much supportive data, pharmacogenetic optimization of heart failure treatment regimens is not yet a reality. In order to attenuate the rising burden of heart failure, particularly in the context of the recent paucity of new effective interventions, there is an urgent need to extend pharmacogenetic knowledge and leverage these associations in order to enhance the effectiveness of existing heart failure therapies. This review focuses on the current state of pharmacogenomics in heart failure and provides a glimpse of the aforementioned future needs.

Adrenergic receptor gene polymorphism and left ventricular reverse remodelling after cardiac resynchronization therapy: preliminary results

AIMS

Several factors can influence the extent of left ventricular (LV) reverse remodelling after cardiac resynchronization therapy (CRT) in patients with heart failure (HF). Polymorphism in genes involved in cardiac remodelling, namely beta-adrenergic receptors (ARs), may have a role. We studied the influence of beta-1 Arg389Gly, beta-2 Arg16Gly, and beta-2 Gln27Glu ARs gene polymorphisms on the magnitude of reverse remodelling response to CRT and its possible correlations with the incidence of appropriate implantable cardioverter-defibrillator (ICD) shocks.

METHODS AND RESULTS

Beta-ARs were assessed in 101 patients with HF due to idiopathic (50.5%) or ischaemic (49.5%) dilated cardiomyopathy, undergoing CRT for standard indications [left ventricular ejection fraction (LVEF) 23.5 ± 7.5%, QRS ≥ 120 ms]. Left ventricular ejection fraction was measured by echocardiography at baseline, 6 months after CRT, and periodically afterwards. The LVEF change from baseline was of 3.1 ± 11 units among Gln27Gln, 8.3 ± 10.4 units among Gln27Glu, 11 ± 6.4 units among Glu27Glu carriers (P = 0.018 for Gln27Gln vs. Glu27Glu carriers), and 8.8 ± 9.8 units among Gln27Glu + Glu27Glu carriers (P = 0.006 vs. Gln27Gln). Gln27 homozygotes had a higher incidence of appropriate ICD shocks for fast ventricular tachycardia/ventricular fibrillation.

CONCLUSION

Beta-2 Gln27Glu ARs gene polymorphism may influence LV reverse remodelling after CRT with Glu27Glu carriers showing the greatest improvement. It may also influence the incidence of malignant ventricular tachyarrhythmias.